Social effects on age-related and sex-specific immune cell profiles in a wild mammal

Evidence for age-related changes in innate and adaptive immune responses is increasing in wild populations. Such changes have been linked to fitness, and knowledge of the factors driving immune response variation is important for understanding the evolution of immunity. Age-related changes in immune profiles may be owing to factors such as immune system development, sex-specific behaviour and responses to environmental conditions. Social environments may also contribute to variation in immunological responses, for example, through transmission of pathogens and stress arising from resource and mate competition. Yet, the impact of the social environment on age-related changes in immune cell profiles is currently understudied in the wild. Here, we tested the relationship between leukocyte cell composition (proportion of neutrophils and lymphocytes [innate and adaptive immunity, respectively] that were lymphocytes) and age, sex and group size in a wild population of European badgers (Meles meles). We found that the proportion of lymphocytes in early life was greater in males in smaller groups compared to larger groups, but with a faster age-related decline in smaller groups. By contrast, the proportion of lymphocytes in females was not significantly related to age or group size. Our results provide evidence of sex-specific age-related changes in immune cell profiles in a wild mammal, which are influenced by the social environment

Early-life effects on telomere dynamicsin European badgers (<i>Meles meles</i>)

Despite extensive evidence of senescence, the decline in performance with age, in wild populations, the drivers ofindividual variation in senescence patternsare still unresolved. In this thesis,I study how early-life environmental, genetic and transgenerational effects contribute to individual variation in senescence patterns, using telomere dynamics,ina wild population ofEuropean badgers (Meles meles).I discovered that telomere length forms a complex relationship with age,withboth decreases and increases in telomere length that cannot be fully explained by measurement error. Telomere length was not sex-specific, but early-life telomere length predicts survival to adulthood (&gt;1 year old) and lifespan. Within-individual changes in telomere length could be due to age-related changesin leukocyte cell composition in response to social conditions. While variation in (early-life)telomere length was associatedwith the abundance and variation in food availability, andnatal but not adultsocial conditions, I found no evidence for heritability of telomere length or transgenerationaleffects, through parental age at conceptioneffects. Additionally, individuals experiencingmatching early-and later-life conditions had longer lifespans,even though there was only moderate autocorrelation in environmental quality, but this also depended on the mean environmental qualityacross adulthood. Ialsodeveloped a novel approach to the analysis of long-term studies, termed slicing, which overcomes problems with confounding effects and cross-classified data structures.My research shows that individual variation in telomere length and senescence is a consequence of early-life environmental, not genetic or transgenerational, effects in European badgers. In addition, I show the potential for adaptive responses in anticipation of the adult environment and the importance ofstudying both the mean of and variability in early-life conditions to fully understand the selective pressures on senescence

Early-life effects on telomere dynamicsin European badgers (Meles meles)

Despite extensive evidence of senescence, the decline in performance with age, in wild populations, the drivers ofindividual variation in senescence patternsare still unresolved. In this thesis,I study how early-life environmental, genetic and transgenerational effects contribute to individual variation in senescence patterns, using telomere dynamics,ina wild population ofEuropean badgers (Meles meles).I discovered that telomere length forms a complex relationship with age,withboth decreases and increases in telomere length that cannot be fully explained by measurement error. Telomere length was not sex-specific, but early-life telomere length predicts survival to adulthood (>1 year old) and lifespan. Within-individual changes in telomere length could be due to age-related changesin leukocyte cell composition in response to social conditions. While variation in (early-life)telomere length was associatedwith the abundance and variation in food availability, andnatal but not adultsocial conditions, I found no evidence for heritability of telomere length or transgenerationaleffects, through parental age at conceptioneffects. Additionally, individuals experiencingmatching early-and later-life conditions had longer lifespans,even though there was only moderate autocorrelation in environmental quality, but this also depended on the mean environmental qualityacross adulthood. Ialsodeveloped a novel approach to the analysis of long-term studies, termed slicing, which overcomes problems with confounding effects and cross-classified data structures.My research shows that individual variation in telomere length and senescence is a consequence of early-life environmental, not genetic or transgenerational, effects in European badgers. In addition, I show the potential for adaptive responses in anticipation of the adult environment and the importance ofstudying both the mean of and variability in early-life conditions to fully understand the selective pressures on senescence

Early-life effects on telomere dynamicsin European badgers (<i>Meles meles</i>)

Despite extensive evidence of senescence, the decline in performance with age, in wild populations, the drivers ofindividual variation in senescence patternsare still unresolved. In this thesis,I study how early-life environmental, genetic and transgenerational effects contribute to individual variation in senescence patterns, using telomere dynamics,ina wild population ofEuropean badgers (Meles meles).I discovered that telomere length forms a complex relationship with age,withboth decreases and increases in telomere length that cannot be fully explained by measurement error. Telomere length was not sex-specific, but early-life telomere length predicts survival to adulthood (&gt;1 year old) and lifespan. Within-individual changes in telomere length could be due to age-related changesin leukocyte cell composition in response to social conditions. While variation in (early-life)telomere length was associatedwith the abundance and variation in food availability, andnatal but not adultsocial conditions, I found no evidence for heritability of telomere length or transgenerationaleffects, through parental age at conceptioneffects. Additionally, individuals experiencingmatching early-and later-life conditions had longer lifespans,even though there was only moderate autocorrelation in environmental quality, but this also depended on the mean environmental qualityacross adulthood. Ialsodeveloped a novel approach to the analysis of long-term studies, termed slicing, which overcomes problems with confounding effects and cross-classified data structures.My research shows that individual variation in telomere length and senescence is a consequence of early-life environmental, not genetic or transgenerational, effects in European badgers. In addition, I show the potential for adaptive responses in anticipation of the adult environment and the importance ofstudying both the mean of and variability in early-life conditions to fully understand the selective pressures on senescence

Early‐life seasonal, weather and social effects on telomere length in a wild mammal

Early-life environmental conditions can provide a source of individual variation in life-history strategies and senescence patterns. Conditions experienced in early life can be quantified by measuring telomere length, which can act as a biomarker of survival probability in some species. Here, we investigate whether seasonal changes, weather conditions, and group size are associated with early-life and/or early-adulthood telomere length in a wild population of European badgers (Meles meles). We found substantial intra-annual changes in telomere length during the first three years of life (both between and within individuals), with shorter telomere lengths in the winter following the first spring and a trend for longer telomere lengths in the second spring compared to the first winter. In terms of weather conditions, cubs born in warmer, wetter springs with low rainfall variability had longer early-life (3–12 months old) telomere lengths. Additionally, cubs born in groups with more cubs had marginally longer early-life telomeres, providing no evidence of resource constraint from cub competition. We also found that our previously documented positive association between early-life telomere length and cub survival probability remained when social and weather variables were included. Finally, after sexual maturity, in early adulthood (i.e. 12–36 months) we found no significant association between same-sex adult group size and telomere length (i.e. no effect of intra-sexual competition). Overall, we show that controlling for seasonal effects, which are linked to food availability and foraging success, is important in telomere length analyses, and that variation in telomere length in badgers reflects early-life conditions and also predicts first year cub survival